Until recently, network profile URLs were frightening. Five months ago I used one to refer to an active user of Mathematics.

Since a few weeks the URLs are much shorter. Nice! But the old link now redirects me to what I assume is an unrelated user. (Little activity, and no account on Mathematics.)

I think I linked to the author of a question who no longer is a registered user†, and is now displayed as "user6163". That might explain some re-use of network IDs to keep them short. Still then, if doable: the old GUID URL should probably yield a 404 instead?

† Given a Meta post about lost reputation for the old user "Nir", maybe some abuse was taken care of, and the current user is some merged account. But then I'd expect some activity in Mathematics again?

To find your own old URL in Google: search for the URL of, for example, your Stack Overflow profile, hover the "expand" button to the right of the search results to show a preview, and then click "In cache". Some of my profiles were updated too recently. But it only takes one older cached profile to be able to see the old GUID URL underneath your avatar... (A cache of the 24th had the new URL; a cache of the 11th still showed the old URL.)
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ArjanOct 2 '11 at 20:55